Phase assemblage of a 5 year-old cement paste after submission to various high temperature and cooling regime.
Résumé
In case of fire in a structure, concrete undergoes internal transformations that can alter its durability. It is also important to take into account the effect of the cooling regime after temperature exposure on the phase assemblage of the cementitious matrix. An experimental investigation was carried out to investigate the changes of a cement paste, heated up to various temperature up to 1000°C then cooled in water or cooled in air for comparison. Quantitative evolution of phase assemblage is obtained by various techniques (TGA, XRD, NMR and ICP-AES). For both cooling regimes, the hydrated crystallised phases tend to become disordered phases for lower exposition temperature. These phases coexist with anhydrous products for intermediate temperature and these new anhydrous phases become the majority for higher temperature. However, the two cooling regimes show differences. Equilibrium of hydrated aluminate phases is modified, (e.g. AFm/AFt ratio). There are structural modifications of the phases in particular for C-S-H. For water cooling regime, beyond 600°C, a leaching is observed in particular for calcium.
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